PROJECT SUMMARY An effective HIV-1 remains an important but elusive goal. One promising approach to such a vaccine uses sequential immunization to guide B-cell receptor (BCR) maturation. To do so, one first amplifies immature unmutated precursors of a particular class of broadly neutralizing antibodies (bNAbs). These precursor BCR are then shepherded to recognize HIV-1 envelope glycoprotein (Env) using increasingly native Env antigens. Sequential immunization strategies for both VRC01- and V3-glycan-classes of bNAbs are being developed. Here we establish the foundations for using the same general strategy to elicit V2-glycan/apex antibodies. Apex bNAbs have properties that both complicate such an approach but ultimately make success more likely. Specifically these bNAbs bind Env largely through their long, acidic and tyrosine-sulfated heavy-chain CDR3 region. Thus there is less need for extensive somatic hypermutaion characteristic of V3-glycan and VRC01-class bNAbs. However, apart from their long sulfated CDR3 regions, apex bNAbs have few distinguishing features. Here we show that we can elicit antibodies in rats with long tyrosine-sulfated CDR3 regions using anti-sulfotyrosine antibodies as antigens. We propose to optimize this approach and use it in concert with oligomeric forms of Env trimers to elicit anti-apex antibodies. These studies will develop a potentially easier approach to generating broad and potent anti-HIV-1 antisera.